The method of data communication according to the MIDI standard is an asynchronous serial communication method as prescribed in "MIDI 1.0 DETAILED SPECIFICATION DOCUMENT VERSION 4.0," and the data transfer rate used in this method is 31.25 kbit/sec. When one byte (8 bits) of data is to be transferred, one start bit and one stop bit are added thereto, and the data therefore comprises 10 bits in its entirety.
In the data communication according to the MIDI standard, data is handled in the unit of "messages" comprising a plurality of bytes. With reference to FIG. 7, these messages are divided generally into channel messages and system messages, which are further classified into different types of messages, i.e., five types in total. The messages of these types include a channel voice message, channel mode message and system common message each comprising one status byte, and one or two data bytes led by the status.
According to the MIDI standard, up to 16 channels are settable. The status byte includes channel number data indicating a particular channel to which the message is directed. Utilizing the concept of the MIDI channels, therefore, for example 16 musical instruments are individually controllable independently through a single MIDI cable.
The channel voice message shown in FIG. 7 is further classified according to the function as shown in FIG. 8. The note on message included in the classified messages corresponds to "production of sound" which is the most essential of all items of performance data. As seen in FIG. 9 (a), this message is composed of the status byte "9Xh" (wherein h is a symbol indicating that hexadecimal notation is used, and X is a hexadecimal number representing a particular MIDI signal channel and is one of the values 0 to F), and two bytes of data subsequent to the status byte. The first data byte is termed "note number" for controlling the musical interval. The second data byte is called "velocity" for controlling the sound volume.
On the other hand, the note off message corresponds to "cessation of sound" and is composed of the status byte "8Xh" and two bytes of data subsequent thereto as shown in FIG. 9(b). Incidentally, the note on message and the note off message are paired, and a pair of note on and note off messages are identical in note number.
The sound source device to be controlled by MIDI signals starts to produce a sound with specified musical interval, sound volume and tone color in response to one message, and ceases producing the sound in response to another message thereafter given. In the simplest case, therefore, a specified sound can be continuously produced from the device only for a predetermined period of time by intermittently feeding to the device a message specifying particular musical interval, sound volume and tone color, a message for starting sound production and a message for ceasing the sound production, each at a predetermined time.
In the case where the specified sound is to be produced only for the predetermined period of time with MIDI signals, sound signals need not be continuously given over the period of sound production unlike the sound reproduction by audio tape recorders or the like but MIDI signals need only to be fed to the sound source device intermittently, so that the specified sound can be produced with a greatly reduced amount of data.
Incidentally, MIDI signals are usually stored in a medium in a format adapted for computer communication together with timing data for controlling the output timing of messages.
In recent years, so-called "KARAOKE" apparatus have found wide household and business uses for enjoying singing songs to the accompaniment of music reproduced from disc recording media.
Video disc players having a sound mixing function are conventionally utilized as such KARAOKE apparatus. The sound signal of an accompaniment reproduced from a video disc and the sound signal of a song input from a microphone are mixed together to release the resulting sound from a speaker. Further the images of the corresponding text reproduced from the video disc are projected one after another on the screen of a display in synchronism with the reproduction of sound signal of the accompaniment.
Video discs for KARAOKE each have stored therein a plurality of musical compositions or tunes. Since the accompaniment sound signal and the text image signal for each tune are recorded at the same time as superposed, a very great amount of data is stored for each tune. For this reason, the number of tunes which can be stored in one disc is inevitably much smaller than in other discs, for example, a compact disc wherein the sound signal only is stored.
Accordingly, the conventional KARAOKE apparatus have the drawback of necessitating frequent changes of discs upon request for tunes.